Currently, there is a need for agents to treat harmful bacterial diseases such as, for example, anthrax disease. Bacillus anthracis (Smith, H., Keppie, J. Nature 173, 869-870 (1954)) is considered the causative bacterium of anthrax disease, whose clinical presentation and outcome in humans strongly depend on its way of entry. Generally, cutaneous contact is rarely lethal, while inhalation is more dangerous and serious. Usually inhalation is fatal if not diagnosed early (Hanna, P. Curr. Topics Microbiol. Immunol. 225, 13-35 (1998)). In fact, in mammals infected with anthrax, bacterium spores germinate in alveolar macrophages before migrating to lymph nodes where they multiply (Hanna, P., Acosta, D., Collier, R. J. Proc. Natl. Acad. Sci. USA 90, 10198-10201 (1993)). Vegetative bacteria excrete a tripartite exotoxin constituted by three different polypeptides: protective antigen (PA, 83 kDa), lethal factor (LF, 90 kDa) and edema factor (EF, 89 kDa). Concerted activity of the above three polypeptides succeeds in killing host cells (Bradley, K. A., Mogridge, J., Mourez, M., Collier, R. J., Young, J. A. Nature 414, 225-229 (2001)). PA (Petosa, C., Collier, R. J., Klimpel, K. R., Leppla, S. H., Liddington, R. C. Nature 385, 833-838 (1997)) can bind to an ubiquitously expressed cellular receptor and, after a proteolytic activation, it is cleaved into a 63-kD fragment (PA63) and a 20-kDa (PA20) moiety. PA20 dissociates into medium and allows the PA63 fragment to heptamerize and bind both LF and EF. The resulting complex is engulfed into intracellular compartments called endosomes; this is successively followed by translocation of LF and EF into cytosol (Scobie, H. M., Rainey, G. J., Bradley, K. A., Young, J. A. Proc. Natl. Acad. Sci. USA 100, 5170-5174 (2003)). Once inside the cell LF and EF exert their toxic action. EF is a calmodulin-activated adenylyl cyclase that impairs the host defenses through a variety of mechanisms inhibiting phagocytosis (Leppla, S. H. Proc. Natl. Acad. Sci. USA 79, 3162-3166 (1982)). LF is a Zn2+ dependent protease capable to cleave several mitogen activated protein kinase kinases (MAPKK) (Vitale, G. et al. Biochem. Biophys. Res. Commun. 248, 706-711 (1998); Duesbery, N. S. et al. Science 280, 734-737 (1998)). This cleavage leads to macrophage cell lysis through a mechanism of action not completely known so far. Recently, it has been suggested that in LF-exposed macrophages, apoptosis can be a consequence of p38 MAPK inactivation. This is believed to prevent release of chemokines and cytokines so that immune system becomes unable to respond to the pathogen (Park, J. M., Greten, F. R., Li, Z. W., Karin, M. Science 297, 2048-2051 (2002)).
The lethal action of anthrax toxin can be neutralized at several stages during its entry into the cell. In fact it would be possible to inhibit PA63 processing, pore assembly or binding to receptor; moreover a successful therapeutic treatment could prevent LF or EF binding or their translocation into the cytosol (Sellman, B. R., Mourez, M., Collier, R. J. Science 292, 695-697 (2001)). Nevertheless inhibition of LF protease activity is still the most promising avenue for this harmful disease (Schwarze, S. R., Hruska, K. A., Dowdy, S. F. Trends Cell Biol. 10, 290-295 (2000)).
Inhibition of LF protease activity is believed to be a promising avenue for this harmful disease (Schwarze, S. R., Hruska, K. A., Dowdy, S. F. Trends Cell Biol. 10, 290-295 (2000)). Thus, a continuing need exists for compounds that inhibit lethal factor (LF) protease activity of anthrax toxin that are useful for therapeutic applications.